The present invention relates to disk recording or playback devices having a mechanism for adjusting the tilt of the pickup with respect to the signal bearing surface of the disk.
FIG. 5 is a perspective view of a conventional disk recording or playback device. A chassis 1 has mounted thereon a turntable 3 for placing a disk 7 thereon as is already known, and a pickup 2 movable toward or away from the turntable 3. The pickup 2 is provided with an objective lens 22 on its upper side and guided for movement by two guide rods 4, 4 on the chassis 1. Each guide rod 4 has its opposite ends fitted in respective brackets 9 on the chassis 1.
FIG. 8 is a rear view of the disk 7. The disk 7 has formed in its signal bearing surface a plurality of pits 73, 73 arranged circumferentially thereof. The reflected beam differs in intensity when a laser beam is projected on the pit 73 and when it is projected on a portion other than the pit 73, whereby a digital signal comprising 0 and 1 is reproduced.
In recent years, DVDs (digital versatile disks) are proposed which have signals recorded thereon at a high density. The proposed disk has a reduced spacing H between the pits 73, 73 radially of the disk as shown in FIG. 8.
Accordingly, if the optical axis of the laser beam is slightly inclined with respect to the signal bearing surface of the disk 7, the beam is likely to impinge on the pit 73 at an incorrect position, failing to reproduce the signal correctly.
It has therefore been proposed to provide a mechanism on the chassis 1 for adjusting the tilt of the pickup 2 and to finely adjust the tilt of the pickup 2 for smooth playback of the DVD in the process for fabricating the disk recording or playback device.
FIG. 6 is a view in section taken along the line Axe2x80x94A in FIG. 5. The disk 7 is transported as placed on a tray 5 onto the chassis 1. The tray 5 is moved horizontally by a drive mechanism (not shown) from outside the chassis 1 to above the chassis 1 and then lowered to place the disk 7 on the turntable 3.
Two adjusting screws 6, 6 extend upward through the chassis 1 in screw-thread engagement therewith respectively for opposite ends of the guide rod 4 to support these ends of the guide rod 4 from below with the upper ends of the adjusting screws 6. A compression spring 90 is provided within each bracket 9 for biasing the guide rod 4 downward. The compression springs 90 and the adjusting screws 6 constitute a mechanism for tilting the pickup 2 in a plane containing the direction of movement of the pickup 2 and orthogonal to the upper surface of the chassis 1.
To tilt the pickup 2, one of the adjusting screws 6 is rotated. This lifts the guide rod 4 against the compression spring 90 for tilting. Since the guide rod 4 is tilted, the pickup 2 is also tilted.
FIG. 7 is a plan view of the tray 5. A large disk having a diameter of 12 cm or a small disk having a diameter of 8 cm is selectively placed onto the tray 5. Concentrically formed in the tray 5 are a large recessed portion 51 for the large disk to fit in, and a small recessed portion 52 for the small disk to fit in. The tray 5 has an opening 50 extending from an end portion thereof to both the central portions of the large recessed portion 51 and the small recessed portion 52. The beam of the pickup 2 is projected on the disk 7 through the opening 50.
However, the conventional adjusting mechanism has the following problem.
With the conventional adjusting mechanism, the compression spring 90 biases the guide rod 4 downward and therefore increases the height of the bracket 9 by an amount corresponding to the height of the spring 90, with the result that the upper end of the bracket 9 is positioned at a higher level than the upper surface of the pickup 2. Accordingly, the bracket 9 needs to be positioned within the opening 50 of the tray 5 as lowered, and the opening 50 of the tray 5 must be made great.
However, if the opening 50 of the tray 5 is great, the small disk is likely to slip off the tray 5 when placed into the small recessed portion 52 as positioned partly in the large recessed portion 51 in error. In the absence of the tilt adjusting mechanism, the mechanism need not be positioned in the opening 50, which therefore can be smaller. The tilt adjusting mechanism is nevertheless indispensable to the reproduction of signals as recorded on the disk at a high density as previously stated.
An object of the present invention is to provide a disk recording or playback device which has a mechanism of reduced height for adjusting the tilt of the pickup and wherein the small disk is prevented from slipping off the tray.
According to the invention, an adjusting mechanism for altering the tilting angle of a guide rod 4 in a plane containing the direction of movement of a pickup 2 and orthogonal to an upper surface of the chassis 1 comprises a spring member having one end attached to the chassis 1 and the other end in contact with the guide rod 4 for biasing the guide rod 4 toward an adjusting member, and means for restraining the guide rod 4 from deflecting in a plane containing the direction of movement of the pickup 2 and approximately parallel to the upper surface of the chassis 1.
The spring member and the restraining means each have an upper end positioned at a lower level than the lower surface of a tray 5 having a disk 7 as placed on the turntable 3.
Thus, the adjusting mechanism is positioned below the tray 5 when the disk 7 is placed on the turntable 3. Since the adjusting mechanism need not be disposed within an opening 50 of the tray 5, the opening 50 can be made smaller. This obviates the likelihood that a small disk will slip off the tray 5.
Further because the height from the chassis 1 to the tray 5 can be diminished, a device of reduced overall thickness is available.